The Journal of Neuroscience, February 1, 2000, 20(3):1129-1141
Department of Neurobiology and Psychology, and Brain Research
Institute, University of California-Los Angeles, Los Angeles,
California 90095
In the current paper it is proposed that short-term plasticity and
dynamic changes in the balance of excitatory-inhibitory interactions
may underlie the decoding of temporal information, that is, the
generation of temporally selective neurons. Our initial approach was to
simulate excitatory-inhibitory disynaptic circuits. Such circuits were
composed of a single excitatory and inhibitory neuron and incorporated
short-term plasticity of EPSPs and IPSPs and slow IPSPs. We first
showed that it is possible to tune cells to respond selectively to
different intervals by changing the synaptic weights of different
synapses in parallel. In other words, temporal tuning can rely on
long-term changes in synaptic strength and does not require changes in
the time constants of the temporal properties. When the units studied
in disynaptic circuits were incorporated into a larger single-layer
network, the units exhibited a broad range of temporal selectivity
ranging from no interval tuning to interval-selective tuning.
The variability in temporal tuning relied on the variability of
synaptic strengths. The network as a whole contained a robust
population code for a wide range of intervals. Importantly, the same
network was able to discriminate simple temporal sequences. These
results argue that neural circuits are intrinsically able to process
temporal information on the time scale of tens to hundreds of
milliseconds and that specialized mechanisms, such as delay lines or
oscillators, may not be necessary.